In prior known combination locks, there is provided a cam concentrically arranged with tumbler wheels.
The tumbler wheels are journaled in coaxial relation for rotation within a lock casing on a tubular arbor or tumbler post projecting inwardly from the front wall of the casing. The lock dial, which usually has 100 peripheral calibration marks thereon, is affixed to a dial spindle which extends through the bore of the tumbler post and has keyed to the inner end thereof a disk-like drive cam which is likewise arranged coaxially with and spaced rearwardly from the tumbler wheels. A drive pin projects forwardly from the drive cam and has a lost motion connection through a conventional fly with the rearmost tumbler wheel to drive the tumbler wheel in selected relation to the drive cam. A similar lost motion connection is provided between each of the successive tumbler wheels so that each of the tumbler wheels may be driven upon predetermined rotation of the drive cam. The drive cam and tumbler wheels are rotatable by mechanical engagement with the lock dial.
In some conventional locks, a fence lever is pivotally connected near one end of a reciprocative bolt, slidably supported in the lock casing, and provided with a depending nose near the opposite end which is designed to ride upon the drive cam periphery. This lever has a bar or fence projecting laterally in overlying relation with the peripheries of the tumbler wheels. The position of the fence in relation to the length of the fence lever nose is usually such that the fence is spaced slightly from the peripheries of the tumbler wheels when the fence lever nose is riding on the drive cam periphery. The cam includes a gate indented from its perimeter which is adapted to receive the nose which is mechanically connected to the latch mechanism. The tumbler wheels each provide a fence gate located at a proper rotational position of each tumbler wheel. A fence is provided connected to the nose such that the nose cannot enter the cam gate unless the fence is able to enter all fence gates of the tumbler wheels, i.e., the tumbler wheels have all been precisely aligned according to the number combination for the particular lock.
It has been recognized that the fence must be elevated from the tumbler wheels during manipulation of the combination dial to prevent surreptitious "feeling" of the position of the fence gates for the tumbler wheels to ascertain the correct combination numbers. However, in these prior locks, the nose rode on the cam surface which permitted a sensory feel of the fence "drop" while the nose was within the nose gate area of the cam. In other words, when the cam is without support within the cam gate area, the fence dropped to the highest tumbler wheel surface. A skilled person, following a precise procedure can manipulate the dial to determine the position of the fence gates for the tumbler wheels.
Various modifications in combination lock structures have heretofore been resorted to, to defeat detection of the lock combination in this manner. Among these is the lock structure disclosed in prior U.S. Pat. Nos. 2,575,674 and 2,807,954 to Harry C. Miller, wherein a guard or shielding slide is mounted on the rear face of the driving cam and has curved end portions conforming to the curvature of the drive cam periphery which normally overlaps the drive cam gate and forms a smooth continuation of the drive cam periphery to support the fence lever nose when the drive cam gate is in registry with the fence lever nose. An inner spindle extends through the dial spindle and is coupled at its inner end to the shielding slide at its outer end to a knob which is in exposed condition, whereby upon rotation of the knob and inner spindle, the slide may be shifted radially of the drive cam to expose the drive cam gate for reception of the fence lever nose. When the shielding slide is in projected position exposing the drive cam gate to entry of the fence lever nose, stop members on the lock casing are disposed in the path of movement of a portion of the slide to limit rotation of the drive cam to an extent which will prevent detection of contact points for the fence lever nose.
It has been determined, however, that the security of this lock may be adversely effected in time if the portion of the shielding slide which is projected beyond the drive cam periphery becomes worn, as by abrasion against adjacent surfaces of the lock casing. It is possible that the projected end surface of the shielding slide may become worn to a depth equal to the spacing of the fence from the tumbler wheel peripheries when the fence lever nose engages the driving cam periphery. In such a case, the slide may be only partially projected from the position wherein it shields the drive cam gate to lower the fence into contact with the tumbler peripheries and lower the fence lever nose into at least the entrance to the drive cam gate without projecting the slide sufficiently to permit the stop member to limit rotation of the drive cam. In this condition, the dial could be manipulated to permit sensing of the contact points and detection of the combination of the lock.
Combination locks have also been designed to elevate both the nose and the fence from the cam surface and the tumbler wheels respectively during manipulation, while causing a forced descension of the cam nose once each dial rotation to allow engagement between the cam nose and the cam gate if the tumbler wheels are properly aligned. If the tumbler wheels are all aligned properly, the descension of the cam nose into the cam gate is successful and the latch can be mechanically unlatched. Such locks are disclosed in U.S. Pat. Nos. 3,045,466; 4,756,176; and 4,910,981.
However, in accomplishing this task these devices require multiple springs or multiple lever arms and are more costly and complicated than the device offered by the present invention.